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Cruisers and Destroyers
1. Assumptions.
(a) Offensive action by cruisers and destroyers during a general engagement will be as directed by the O. T. C., either by signal or in accordance with a battle plan.
The major offensive normally will be launched against the enemy battle line.
Primary attack weapons for such an offensive will be torpedoes, launched from the most effective relative position possible for cruisers and destroyers to attain. A torpedo offensive usually will be launched at some time after the opposing battle lines are engaged in gunfire action with their main batteries.
Secondary attack weapons may be gas shell or gas (smoke) screens.
An indirect and contributory means of attack consists of laying smoke screens at times and in positions prescribed by the O. T. C., in order to assist own battle line's gunfire against that of the enemy.
In driving home an offensive, gunfire, torpedoes, gas, smoke and ramming may be directed against opposing enemy ships.
(b) Defensive action by cruisers and destroyers during a general engagement normally will be an ever-present task, unless and until an offensive movement is ordered by the O. T. C.
Such action will be taken against enemy units that are attempting to attain favorable relative positions for attacking own battle line.
Enemy cruisers and destroyers carrying or supporting a torpedo threat, enemy ships carrying or supporting a mine threat, and aircraft carrying or supporting a torpedo or bombing threat, will be opposed primarily with gunfire.
Surface craft may be opposed by use of torpedoes or ramming.
Enemy submarines will be opposed by depth charges from destroyers, or by gunfire from, or ramming by, cruisers and destroyers.
Enemy gas attack usually will be defended against only by local means -- masking of personnel, maneuvering to clear gassed areas, and decontamination. Gunfire may be undertaken against ships of similar type or smaller ships making such an attack.
Smoke screens may be used in own defense, or as directed by O. T. C. to defend own battle line against gunfire, bombing or torpedo attacks.
2. Problems Involved.
Of the many problems involved during the course of a general action, those that become pressing to the commander of cruisers and destroyers are:
(a) Prior to and at the time of attack -
(1) Where should I be to start my offensive?
(2) Where should I proceed with my attack?
(3) Can I get to the most favorable attack position with an adequate force?
(4) If I can't get there with an adequate attack force, where is the next most favorable attack position that I can reach?
(b) If on the defense -
(1) Where should I be?
(2) How can I get there in time?
3. Initial Considerations.
In order to arrive at some means of solving the foregoing inter-related problems, it is requisite that the capabilities and limitations of cruisers and destroyers and their possible opponents be surveyed as briefly as is relevant.
At the outset, it may be considered almost axiomatic that during a general daylight action, ships appreciably weaker in fire effect and armor protection ordinarily should not undertake an offensive against, or come within effective gun range of main batteries of, larger ships, unless the latter are so engaged that they probably cannot use their main batteries against the weaker ships.
As a second major consideration, it should be recognized that in sea conditions other than smooth, ships probably will suffer a decrease in designed maximum speed when heading into the sea; that in such conditions, the decrease usually will be inversely proportional to the size of the ships; and that such loss of designed speed may have a decisive influence on the ability of cruisers and destroyers to reach a desired relative position "in time".
With these tow limitations in mind, attention may be directed next to the weapons used in a general action by cruisers and destroyers. Principle offensive weapons available have been assumed to be torpedoes, gas and smoke screens. With regard to defensive weapons, it has been assumed that gunfire, depth charges, torpedoes, ramming, and smoke screens will be employed against various types of opposition.
Surveying the possible employment of these weapons, it is concluded that:
(a) Some elemental discussion appears to be necessary with regard to the capabilities and limitations of torpedoes and their control;
(b) Similar treatment with respect to smoke screens will be of assistance;
(c) Since gunfire against ships and aircraft is discussed in "Fire Action" (issued by the War College), there is not need to further develop that subject in detail here, but it may be commented on with regard to possible positions from which gunfire may be most effective at the point of contact;
(d) Evaluation of the use of depth charges may be confined to a study of possible submarine attack positions;
(e) Ramming is a subsidiary and self-evident weapon, requiring little comment.
4. Method of Treatment.
After analysis of the initial considerations it is believed that a reasonable correlation of the various capabilities and limitations of cruisers and destroyers will be served by studying, in order, the employment of these ships in defense of own battle line, and in attacking enemy battle line. As a first step in visualizing such employment, a general survey of the elements involved in torpedo fire will be undertaken. Elements involved in the use of other weapons may, it is considered, logically be included in a study of the employment of cruisers and destroyers in battle.
5. Elements of Torpedo Fire.
(a) Torpedo Types and Armaments.
For purposes of illustration throughout the text, certain characteristics of the types of torpedoes used in War College games are tabulated, as follows:
| Type | Speed | Range | Carried by * |
| A | 26 | 17,000 | Cruisers, Destroyers |
| B | 28 | 16,400 | Cruisers |
| C | 27 | 13,500 | Destroyers |
| E | 30 | 6,000 | Aircraft |
| F | 35 | 3,500 | Submarines |
| G - X | 27 | 15,000 | Cruisers, Destroyers, Submarines |
| G - Y | 34 | 10,000 | " |
| G - Z | 46 | 6,000 | " |
| H - Y | 32.5 | 9,000 | Submarines |
| H - Z | 46 | 4,000 | " |
* Torpedo armaments and the value of torpedo hits as used at the War College may be referred to in, respectively, War College publications "Fleets" and "Maneuver Rules".
(b) Problems of Torpedo Control
Plate 1 shows a basic triangle upon which calculations for torpedo fire are predicated. The torpedo director is an instrument designed to solve this triangle. Known elements of the triangle are the line of sight, the firing range and the speed and range of torpedo. The unknown elements are the course and speed of the target. An estimate of those unknown elements, together with known elements, is set on the torpedo director which then automatically gives a solution of the required sight angle or base torpedo course, as well as other desirable elements. Gunfire has a similar triangle, but with the side TH, or run of target ship, much less. This si shown by a compares of the figures given on Plate 1.
A further comparison between gun and torpedo fire, illustrative of the problems of torpedo control, is interesting. The time of flight of a torpedo with a run of 12,000 yards is 12.9 minutes for a 28-knot torpedo and 13.0 minutes for a 26-knot torpedo. During this period a target can go on a straight course 7,740 yards and 8,340 yards respectively at 18 knots, or can make a radical change of course and speed and be over 12,500 yards from the point of intercept. Even when the target ship does not avoid the torpedoes by such a great distance, the comparatively slow speed, limited range and small number of torpedoes often permit the target ship to avoid them even when they are sighted fairly close aboard, or to run away from them when they approach from abaft the beam. A BLUE 14"/45 gun has a time of flight of 37 ½ seconds at a mean velocity of about 1,220 knots with an effective range of 23,000 yards, as compared with one of the best torpedo's 12.9 minutes at 28 knots and a run of 12,000 yards. The gun has an extreme range of 33,000 yards as compared to 17,000 yards for the longest-range torpedo. In addition, the gun may fire a number of ranging shots and be spotted on and still fire 75 to 90 shots thereafter; the torpedo will have no opportunity or practical capability for ranging shots or spotting and will have only 1 shot per tube. A battleship can fire from 800 to 1200 heavy calibre shots in many successive salvos; a destroyer or cruiser can fire 6 to 12 torpedoes in one or two salvos, or a division of destroyers or cruisers 24 to 48 torpedoes, or a squadron of destroyers 108 to 153 torpedoes.
To remedy these inherent deficiencies of torpedoes as compared with guns is the problem of modern torpedo control A great deal of analysis, experimentation, and material improvement has been made in torpedo control. As a result it may be said that probably the most effective results are obtained in torpedo fire by the use of salvo firing of maximum volume, with dispersion (or spread) from a favorable firing position. Discussion of these various elements follows.
(c) Volume of Fire.
Other factors being equal, the chances of torpedoes hitting will occur in direct proportion to the number fired in a salvo. For purposes of limiting our study to the factors of time and relative position, it will be assumed herein that when a decisive issue is joined, cruisers and destroyers ordered to attack with torpedoes will make one determined, fierce assault with all torpedoes, and will be actuated by the utmost perseverance in enemy destruction.
It is recognized, in making an assumption that all torpedoes will be fired, that the conduct of war is not governed by such a premise. Commanders may decide on feints, threats and secondary attacks, designed to influence the enemy's mind and action adversely and involving the firing of either a few or no torpedoes at a retirement. Or opportunities may occur during a general action of injuring the enemy by the fire of one or two torpedoes without jeopardizing the success of the general plan -- such as firing torpedoes close aboard at an enemy carrier, cruiser, destroyer, submarine, or ship of comparatively inferior military value. Whether an expenditure of torpedoes in these cases may be considered by a commander to be justified will depend on his trained judgement as to the relative necessity of furthering the general plan, and of injuring the enemy to the utmost.
(d) Firing Positions.
Firing positions are located by the target angle and the firing range.
A target angle will serve the most efficient torpedo fire when it is such as to permit:
(1) the torpedoes of a salvo to make as many actual hits as possible,
(2) torpedoes of a salvo to reach as large a percentage of the entire length of the target selected as possible, and
(3) the greatest errors in assumed enemy course and speed, or the greatest changes in enemy course and speed after torpedoes are fired, and still permit them to reach and hit the target when fired in a salvo.
The target angle which probably will make the most actual hits, if the torpedoes will reach and the enemy does not maneuver, is where a "closed" target is presented. This will depend on the enemy's formation and will be a different target angle for each different formation. The target angle where the torpedoes will reach the most effectively is 0º, or dead ahead. The target angle which will reach and hit the best, in spite of errors in sight bar course and speed or of enemy maneuvers, is where the track angle is approximately 90º. It may be state, without important inaccuracies, with reference to any target -- single ship or any formation or group of ships -- that the single target angle which most closely meets all of the above conditions for a single salve is the angle whose tangent is the torpedo speed divided by the enemy speed, or which gives a track angle of 90º. When a number of destroyers or cruisers in formation are firing approximately simultaneously, the foregoing solution will be fulfilled practically when the middle firing ship is on the bow of the middle ship of the target an angle = tan-1 St/So [ie Torpedo Speed / Target Speed]. This target angle is shown on Plate 2.
Firing Range.
The distinction between Firing Range, Effective Range, and Range of Torpedo requires clarification. Firing Range is the distance from the firing ship to the target ship at the instant of firing. The Effective Range of a torpedo, when fired at a particular target ship on any particular target angle, is the maximum firing range at which that torpedo can be fired and just reach the target ship if the target ship continues at its initial course and speed. These are the practical definitions. They are illustrated on Plate 1. With target angles so that the target ship is continually approaching the firing position, the Effective Ranges are greater than the Range of the Torpedo. With other target angles the Effective Ranges are less than the Range of the Torpedo. For example, when the target ship is heading directly for the firing position the Effective Range is greatest, and when heading directly away the Effective Range is least. The Effective Range depends on the target angle, the Range of the Torpedo, the speed of the torpedo, and the speed of the target ship. Plate 3 shows the Effective ranges at all target angles, with the target ship at speed 18, for types of torpedoes carried by cruisers and destroyers.
It is apparent that the Firing Range should never exceed the Effective Range. For practical purposes it should be considerably less than the Effective Range, in order to allow for errors in sight bar enemy course and speed and changes therein after firing. The shorter the range the less the run of torpedo and, consequently, the less opportunity an enemy has to maneuver to avoid the torpedo, and the denser the salvo in many cases.
The Firing Range should be as short as possible -- how short is difficult to say when approaching under gunfire or other opposition. Just how far, for example, a destroyer can go in and not get sunk before firing its torpedoes cannot be determined by fixed rules. One guide, advocated for destroyers, is to continue the approach until enemy shells are falling regularly and his fire in beginning to be effective. Another consideration here is the possibility that hits made by fragments of detonating projectiles (or of bombs) up to a distance of at least 100 feet, may be capable of occasionally causing the detonation of cast TNT carried in thin containers, such as torpedo warheads, depth charges or mines. The detonation of one warhead may be expected to detonate the warheads of other torpedoes in the same multiple tube. Similar action may be expected in depth charges or mines on tracks. The effect of TNT warheads, depth charges or mines detonating on board ship is estimated to approach very closely the effects of large bombs containing the same weights of high explosive. The location of such detonated TNT charges would govern the damage to the ship as a whole.
In summary, it may be stated that the ideal firing position is where the middle ship of a firing unit is at the target angle = tan-1 St/So [ie Torpedo Speed / Target Speed] on the middle ship of the target, ie, where the track angle is 90º, and at the shortest practicable firing range within effective range. However, the accomplishment of a timely, concentrated and coordinated attack on the right target with many torpedoes in salvo at the shortest practicable firing range within effective range is more important than the attainment of an ideal firing position.
(c) Enemy Course and Speed.
Accuracy in the solution of problems of torpedo fire depends on the accuracy with which the enemy course and speed is determined. This is a problem not only in torpedo fire, but also in gunfire. In torpedo fire, however, the greater time of flight makes it of more significance.
A completely satisfactory means within destroyers and cruisers to determine enemy course and speed for purposes of torpedo control has not yet been devised. Isolated ships and aircraft may have good opportunities of observing and reporting such enemy course and speed. Good tactical scouting often may remedy this defect in torpedo control.
It is believed that the most acceptable sight bar course and speed to set on a director, or to use on the maneuver board, will generally be the closest estimate that can be obtained of the enemy course and speed at the instant of firing. If this assumption holds, errors in the assumed enemy course and speed, or maneuvers by the target, can be corrected by intelligent methods of salvo firing with dispersion (or spread). The efficacy of a single salvo of given spread in minimizing the errors of sight bar course and speed will depend on the firing position attained, both as regards target angle and firing range. The nearer to the best target angle and the shorter the range, the more efficient the salvo should be in this respect.
(f) Salvo Firing.
Firing by salvo, which involves the firing of a number of torpedoes from a single firing ship simultaneously, or approximately so, will be considered herein as the normal method of torpedo fire. An ideal salvo:-
(1) will permit as many torpedoes as possible to hit,
(2) will permit the hitting of as many ships as possible of the selected target, and
(3) will permit as many torpedoes as possible to hit as many ships as possible, irrespective of the target's maneuver to avoid them or errors in sight bar course and speed.
For as many torpedoes as possible to hit, the salvo should be dense. For many ships of the target to be hit the salvo should be wide as well as dense. To hit, irrespective of the target's maneuver or errors in sight bar course and speed, the salvo must be wide.
The elements of width and density, as considered above, are incompatible. No single salvo, embodying ideal width and ideal density at the same time, can be designed. Then it is realized that target angle, firing range, volume of fire, length and character of target formation and number of firing units, all conspire to complicate the problem, it may be seen that a compromise between width and density is apparently required. A compromise might be approached by saying that if the target is free to maneuver, a wide dispersion of torpedoes is desirable. This would be the case in an unsupported attack. If the target is not free to maneuver, a dense salvo may be preferable. This would be the case when the target is under fire of own battle line and the enemy has the choice between harmful effects of maneuver on his own main battery gunfire and certain heavy damage from torpedoes. But such a rule is difficult to apply. Another method of compromise is to select a single dispersion angle and use it on all occasions.
Dispersion in a torpedo salvo is accomplished by firing each torpedo on a different course so as to cover a front which increases in width with length of torpedo run. Such a salvo is defined as a spread. Spread, as a term, also is used to indicate the angle of divergence of the entire salvo - as a 20º spread. Standard spread generally prescribed for straight and virtual straight methods of fire is 20º, for curved fire ahead 22º.
Offset is the angle by which a torpedo track diverges from the director torpedo track. To cover a wide range of maneuvers by a group of target ships, salvos may be offset to the target's rear by a pre-determined angle, * [* U. S. F. 32] dependent on the target angle.
While there are difficulties entailed, as noted above, in a single salvo, it is obvious that ideal width and density may be approached by the simultaneous fire of a number of salvos from many firing units from widely different directions at the same target. Matters may also be improved if a point of aim toward the center of the enemy formation is selected, as enemy ships, other than those aimed at, may then be struck if a turn is executed by the enemy.
To illustrate width and density, two salvos will be examined, one leaning more to density and the other to width.
On Plate 4, there is shown what is probably the simplest way of firing salvos, where 4 destroyers in formation fire 6 Type C torpedoes on each broadside, each destroyer directing all 6 of her torpedoes at one particular target ship, without the application of spread. The 4 destroyers fire at 4 adjacent target ships - destroyer speed 30 knots, target speed 18, firing period 30 seconds. With the target angle and firing range shown, the dispersion (or width) will be 1800 yards at 7000 yards run and 2100 yards at 13,000 yards run. This will give an average density of 1 every 163 yards at 7000 yards run and 1 every 190 yards at 13,000 yards run. With target ships 200 yards long, many ships within the limits of the pattern at any run of torpedo will be hit unless they maneuver individually. If they maneuver in concert to avoid the salvo entirely, they must turn at least 80º toward, or 50º away. These results, of course, change as either the target angle or firing range changes. On Plate 4 the target angle is close to the ideal. As the firing range decreases the density gets better, although there is not much difference, as the dispersion angle is only 3º. This salvo is strong on density, but suffers in width.
On Plate 5 is shown the same 4 destroyers firing in the same relative position, but using curved fire ahead (or virtual straight fire), each ship selecting individual target ships in the leading half of the enemy formation. Gyros are set to give a dispersion angle of about 4º between torpedoes when one broadside is fired and 2º when both broadsides are fired simultaneously. This gives a spread from each destroyer of 20º or 22º. The salvos are bodily offset 10º toward the target's rear in accordance with standard instructions for this situation. Under the conditions shown on Plate 5, the dispersion at 7000 yards run is 5200 yards as compared with 1800 yards by the previous method, and 8900 yards at 13,000 yards run as compared with 2100 yards by the previous method. The resulting density is 1 every 473 yards at 7000 and one every 800 yards at 13,000 yards, as compared with 163 yards and 190 yards respectively. Ships 200 yards long may steam through such a salvo and may be missed completely, particularly if they can see the torpedo wakes in time for individual maneuver. If they maneuver in concert to avoid the salvo completely, they will have to turn toward at least 120º and away 60º, as compared with 90º and 50º respectively in the previous method. As the firing range decreases, the density by this method gets better. To obtain as good a density as the first method the torpedo run must be no more than 2000 yards. This salvo corrects for much greater errors in sight bar enemy course and speed and much wider changes of enemy course and speed than the previous one. It is weak on density, but strong on width.
In both cases the density, as well as the width, is improved as the number of firing units increases and the target angles become more numerous and more varied; provided, all salvos are directed at the same target at about the same time. This latter contingency also tends to give a criss-cross pattern which is hard to avoid once the salvo areas is entered. Plate 6 shows a squadron of three divisions using the first of these methods. It is seen that the density and width are improved.
These two cases are shown not to prove one method better than the other, but merely to illustrate width and density and the difficulty of embodying both requirements in one salvo.
Plate 7 shows the largest and most controlled destroyer torpedo attack made during the World War. 31 torpedoes were fired at the British battle line by 13 German destroyers in two salvos. These two salvos were fired almost simultaneously, from good target angles and at firing ranges within effective range. The spread, as measured from a single firing destroyer, was approximately 13 ½º in one case and 9º in the other. About 42% of the torpedoes fired passed through the target formation, but unfortunately the density was not enough. It averaged about 1 torpedo to 500 yards in one salvo and 1 to 200 yards in the other. All the target ships maneuvered clear by division or individual action. No hits were made.
(g) Summary.
Ways and means which have been discussed concerning attainment of concentration of torpedo fire by cruisers and destroyers may be summarized as follows:-
(1) In the general action the target of torpedo fire for cruises and destroyers generally should be in the enemy battle line -- preferably in the same part at the same time, in coordination with own battle line.
(2) The volume of fire in a decisive action has been assumed to include all torpedoes, fired ad nearly simultaneously as possible.
(3) The ideal firing position is where the middle ship of a firing unit is on the bow of the middle ship of the target an angle = tan-1 Torpedo Speed / Target Speed ie, where the track angle is 90º; and where the firing range is the shortest possible within effective range. However, the accomplishment of a timely, concentrated and coordinated attack on the enemy battle line with many torpedoes in salvos at the shortest practicable range within effective range is more important than the attainment of an ideal firing position.
(4) The most acceptable sight bar enemy course and speed is generally the closest assumed course and speed that the enemy is on that the instant of firing. Errors in sight bar course and speed and maneuvers of the target after firing are allowed for by salvo firing with spread.
(5) Both width and density should be considered in designing a salvo of torpedoes -- with to cover errors of sight bar course and speed and target maneuvers, density to insure hits when the enemy enters the salvo pattern. Standard instructions for spread and effect are prescribed for the design of a torpedo salvo. An approach to the ideal in salvo firing will be made by the simultaneous fire of a number of salvos from many firing units from widely different directions. A point of aim toward the center of the enemy formation, or group, or an offset to accomplish the same result, may be considered as nearly always advantageous.
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